1. Technical Field of the Invention
The present invention relates generally to an accumulator fuel injection system equipped with a fuel pressure sensor working to measure the pressure of fuel within an accumulator such as a common rail and a pressure-reducing valve working to reduce the pressure in the accumulator, and more particularly to such a system designed to ensure enhanced reliability of diagnosis of the pressure-reducing valve.
2. Background Art
Automotive fuel injection systems are known which are equipped with an accumulator (also called a common rail) working to supply fuel at high pressure to fuel injectors each for one of cylinders of a diesel engine. Such common rail fuel injection systems are typically designed to control the pressure of fuel in the common rail to be fed to the fuel injectors as a function of operating conditions of the engine.
Specifically, the common rail fuel injection systems typically work to determine a target pressure of fuel in the common rail based on an effort of a vehicle driver on an accelerator pedal and a target quantity of fuel to be injected into the engine and bring a measured value of the pressure of fuel in the common rail into agreement with the target pressure under feedback control.
When the accelerator pedal is depressed to accelerate the vehicle, after which it is released to decelerate the vehicle, the common rail fuel injection system works to decrease the target pressure of fuel in the common rail rapidly. This may cause the measured value of the pressure in the common rail to be much greater than the target pressure.
In order to decrease the pressure in the common rail quickly to the target pressure, Japanese Patent First Publication No. 2004-011448 teaches use of a pressure-reducing valve in the common rail fuel injection systems which works to drain the fuel from the common rail to the fuel tank.
However, typical pressure-reducing valves may be locked in the closed state or fail to drain the fuel from the common rail correctly due to a malfunction of a valve driver. In order to ensure the reliability of operation of the common rail fuel injection systems, it is desirable to diagnose the pressure-reducing valve.